Sydney firefighters hope a huge back burning operation will help contain a bushfire in the city's southwest that may have been deliberately lit before it came dangerously close to suburban homes. The blaze has blackened close to 3000 hectares, including in the Holsworthy military range, and is now the subject of an investigation by NSW Police's Strikeforce Carpi. More than 470 firefighters fought the flames for a third consecutive day on Monday as winds dropped but high temperatures continued to challenge crews. NSW Rural Fire Service Commissioner Shane Fitzsimmons praised the efforts of firefighters who've so far kept homes safe. "At this stage, we still haven't got any serious injury, we haven't got any serious property damage or property loss, which is a remarkable effort," he told 2GB radio. "Probably in the next day or so we can say it's contained but it will be quite a few more days after that before we say it's safe." There's still some back burning required on the fire ground after key work - including south of Menai - had to be suspended due to high winds. On Monday night the RFS revealed 528 homes, three facilities and one outbuilding had been saved. Two homes were damaged and one cubby house was destroyed, according to a survey by assessment teams. Mr Fitzsimmons earlier said it was "extraordinary" there were only minor impacts. The fire started about 2.30pm on Saturday and detectives are trying to determine if there is a link to several spot fires in the Leacock Reserve area on Friday night. "The area where we believe the fire commenced has been forensically examined," NSW Police Acting Superintendent Paul Albury told reporters on Monday. "We have taken a number of statements from people who called the police and fire services in regards to the fire." If the fire was deliberately lit, those responsible could face a punishment of up to 25 years behind bars for the "sickening and reprehensible" act, Mr Fitzsimmons said. But at the moment police were only considering the blaze "suspicious", he added. The RFS cautioned that while the threat had eased, residents in the areas of Voyager Point, Pleasure Point, Sandy Point, Alfords Point, Barden Ridge, Illawong, Menai and Bangor should continue to monitor the situation and be prepared to activate bushfire survival plans should conditions change. The blaze was downgraded from a watch and act to advice alert level about 2am on Monday. Australian Associated Press

"At this stage, we still haven't got any serious injury, we haven't got any serious property damage or property loss, which is a remarkable effort," he told 2GB radio.

"Probably in the next day or so we can say it's contained but it will be quite a few more days after that before we say it's safe."

There's still some back burning required on the fire ground after key work - including south of Menai - had to be suspended due to high winds.

On Monday night the RFS revealed 528 homes, three facilities and one outbuilding had been saved.

Two homes were damaged and one cubby house was destroyed, according to a survey by assessment teams.

Mr Fitzsimmons earlier said it was "extraordinary" there were only minor impacts.

The fire started about 2.30pm on Saturday and detectives are trying to determine if there is a link to several spot fires in the Leacock Reserve area on Friday night.

"The area where we believe the fire commenced has been forensically examined," NSW Police Acting Superintendent Paul Albury told reporters on Monday.

"We have taken a number of statements from people who called the police and fire services in regards to the fire."

If the fire was deliberately lit, those responsible could face a punishment of up to 25 years behind bars for the "sickening and reprehensible" act, Mr Fitzsimmons said.

But at the moment police were only considering the blaze "suspicious", he added.

The RFS cautioned that while the threat had eased, residents in the areas of Voyager Point, Pleasure Point, Sandy Point, Alfords Point, Barden Ridge, Illawong, Menai and Bangor should continue to monitor the situation and be prepared to activate bushfire survival plans should conditions change.

The blaze was downgraded from a watch and act to advice alert level about 2am on Monday.